Athletes and sports stars who suffer career-threatening knee injuries could one day benefit from replacement ligaments grown in the lab.

US scientists bio-engineered anterior cruciate ligaments and used them to repair knee joints in rabbits. Eventually, the researchers hope to treat humans who suffer ruptured ligaments using the technique.

The anterior cruciate ligament sits behind the kneecap and can tear when placed under excessive strain, making it a common sports injury. Each year, an estimated 200,000 people suffer this type of injury in the US alone.

Since the ligament heals poorly on its own, patients sometimes receive ligament transplants from other parts of their own body or from donors. But only so much can be taken without damaging other joints and donated ligaments are in limited supply.
Biodegradable polyester

Cato Laurencin at the University of Virginia, US, and colleagues say a bio-engineered ligament replacement might offer a better alternative to transplants.

The team grew ligament tissue after first weaving together strands of biodegradable polyester using a machine originally designed for textile production. This material, called polylactide, naturally dissolves in the body over time.

Laurencin's team seeded the woven polylactide structure with cells taken from rabbits' anterior cruciate ligaments and cultured them in a dish for two days. Finally, they surgically replaced whole anterior cruciate ligaments in another group of rabbits with the polylactide scaffold material, attaching it to the joint in the same way as a normal ligament.

Twenty-four hours later, the rabbits could already bear their own weight on their knees, and showed fairly normal mobility.

After 12 weeks, researchers removed the engineered structure from the animals' knees for further testing. They found that it could withstand 50% more force than normal transplant tissue can withstand after 30 weeks. This is nevertheless only about one-third as strong as a normal, healthy rabbit ligament.
Blood vessels

Crucially, the scientists also found that collagen-producing cells and blood vessels had grown within the material by the end of the 12 weeks. This suggests that the body had started regenerating healthy ligament tissue within the polylactide scaffold, Laurencin says.

The scaffold structure will start to dissolve within nine months of transplantation and Laurencin says he has "great optimism" that the dissolved scaffold may leave behind a completely regenerated ligament with full strength. He has yet to carry out a full long-term study.

Laurencin also speculates that knee-injury patients might, in future, also receive implants seeded with cells taken from their own bone marrow.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas0608837104)